The present disclosure relates to optical irradiation apparatus, and more particularly to an optical irradiation apparatus which heats an irradiation object or causes photochemical reaction in the irradiation object.
In recent years, attention has been given to techniques of heating an irradiation object or causing photochemical reaction in the irradiation object by optical irradiation. For example, a technique of partially heating a semiconductor or a metal to a temperature equal to or higher than the melting point by optical irradiation to achieve a joint (welding) has been investigated. In addition, a technique of partially heating amorphous silicon on glass by optical irradiation to change the amorphous silicon into microcrystalline silicon in order to enhance a thin film transistor (TFT) is examined. Further, for example, a technique of activating impurities by optical irradiation to enhance properties of a semiconductor doped with the impurities is also investigated.
An optical irradiation apparatus for optical irradiation includes: a semiconductor light-emitting device serving as a light source; and a light collection optical system collecting light emitted from the semiconductor light-emitting device in a predetermined region of an irradiation object. To heat the irradiation object or cause photochemical reaction in the irradiation object, a semiconductor light-emitting device needs to obtain a light output of about 1 W to about 100 W. To uniformly change properties of the optical irradiation region, the light collection optical system needs to show a uniform distribution of the irradiating light intensity in the light collection region.
Examples of known semiconductor light-emitting devices include light emitting diodes (LEDs) and semiconductor laser devices. However, it is difficult for a single LED or semiconductor laser device to obtain a sufficient light output as an optical irradiation apparatus. Thus, a semiconductor light-emitting device needs to be constituted by a plurality of LEDs or semiconductor laser devices, for example, and a coupling optical system coupling light outputs of these devices.
In particular, semiconductor lasers devices have high directivities and can enhance the coupling efficiency of a coupling optical system, and thus, are preferable as a light source of an optical irradiation apparatus. In addition, if a semiconductor laser array in which a plurality of semiconductor laser devices are integrated on one chip is employed, or such semiconductor laser arrays are stacked on one package, size reduction and high output can be achieved. However, when outputs of semiconductor laser devices are coupled together, interference occurs among light beams emitted from the semiconductor laser devices. Accordingly, in a case where the light beams are collected on one place by a light collection optical system, light distribution cannot gradually varies because of interference noise, resulting in a limitation in enlarging a region where uniform light distribution is obtained.
To reduce the interference noise, a technique of converging light emitted from, for example, a semiconductor laser device into light with low interference is proposed (see, for example, U.S. Pat. No. 7,719,738). Specifically, an optical element including: a highly reflective mirror having an aperture; a plano-concave lens provided in the aperture; a light guide for guiding light which has passed through the aperture; and a partially reflective mirror provided at the tip of the light guide is used to convert light emitted from, for example, a semiconductor laser device into light having a low interference property.
The concave lens changes light emitted from a light source such as a semiconductor laser device into light expanding in the radiation direction, and the expanded light enters the optical waveguide. Part of the light which has entered the optical waveguide is emitted directly from the partial reflection mirror. Another part of the light is reflected multiple times between the partial reflection mirror and the high reflection mirror, and then is emitted from the partial reflection mirror. Accordingly, light emitted from the partial reflection mirror is a mixture of various light beams having a difference in optical path length which is an even-numbered multiple of the length of the optical waveguide. By preventing the length of the optical waveguide from being a multiple of ¼ of the wavelength of incident light, it is possible to avoid resonance of light emitted from the partial reflection mirror. As a result, light emitted from, for example, the semiconductor laser device can be converted into light with low interference.
Such use of light with reduced interference is expected to enable light with a uniform distribution to be applied to a wide region.